1. Field of the Invention
The present invention relates to a vibration generator. In the vibration generator of the present invention, a coil and a magnet are arranged along a radial direction. A vibrating body is vibrated in a thrust direction by an interaction between the coil and the magnet.
2. Description of the Related Art
A portable terminal such as a cellular phone or the like includes a vibration generator arranged therein. The vibration generator generates vibration to thereby notify a user of arrival of an incoming call. Different types of vibration generators are available. As one example, there is available a vibration generator in which a vibrating body is vibrated in a thrust direction by an interaction of magnetic fields generated by a coil and a magnet. There have heretofore been proposed various kinds of vibration generators in which a vibrating body is vibrated in a thrust direction.
Japanese Patent Application Publication No. 9-117721 discloses a vibration generator including a vibrating body formed of a weight and a permanent magnet, springs for holding the vibrating body, a drive coil for continuously reciprocating the vibrating body at or near a resonance frequency, a means for supplying an electric signal to the drive coil and a means for transferring the vibration of the vibrating body to the outside via the spring. In this vibration generator, the vibrating body is held by the springs at the thrust-direction opposite sides of the vibrating body.
Japanese Patent Application Publication No. 2011-25221 discloses a vibration generator including: a case defining an internal space; a bracket arranged below the case to support a coil for inducing magnetic fields with an electric current flowing therethrough; a vibrating body having a yoke, a magnet accommodated within the yoke and a weight arranged outside the yoke; and a spring arranged in the upper portion of the case to support the vibrating body. In this vibration generator, a plurality of recess portions is formed on the outer surface of the weight. Rolling members are inserted into the recess portions. The rolling members rotate in contact with the sidewall of the case. In this vibration generator, the deflection of the vibrating body is prevented because the rolling members provided in the weight roll on the side surface of the case as the vibrating body is moved along the side surface of the case.
In the vibration generator disclosed in Japanese Patent Application Publication No. 9-117721, however, regions for arrangement of the springs need to be provided at the thrust-direction opposite sides of the vibrating body. For that reason, the vibration stroke of the weight serving as the vibrating body is small. This makes it impossible for the vibration generator to sufficiently generate vibration. Moreover, the structure in which the springs are installed at the thrust-direction opposite sides of the vibrating body becomes an obstacle in reducing the size of the vibration generator. It is difficult to assemble the structure in which the springs are installed at the thrust-direction opposite sides of the weight. In general, a method of filling a viscous fluid into a vibration generator is used as one of methods for stopping a weight within a short period of time. However, the method of filling the viscous fluid into the vibration generator cannot prevent leakage of the viscous fluid unless the fluid-tightness of a housing serving as an outer shell of the vibration generator is kept high.
In the vibration generator disclosed in Japanese Patent Application Publication No. 2011-25221, the rolling members need to smoothly roll along the side surface of the case. For that reason, the recess portions of the weight, the rolling members and the side surface of the case need to be machined with a high degree of accuracy. The high-accuracy machining tends to impede cost saving.